Really?? I think that everyone here is bright enough to figure out that the cover of the truck's plug latches the 7-way plug in place and that if the plug is not seated properly the cover doesn't latch.
If you have to jimmy with the plug to get it to work, then there is clearly an incompatibility between the two plugs and one needs to be changed. Obviously, that would be the one on the trailer cord since you can but them for around $7. Most of the trailer manufacturers use Bargman plugs/cables and they have known compatibility issues with anything but another Bargman plug, which the truck manufacturers are not using.
Just go buy a Pollak plug, put it on and go camping.